I changed my bonnet badge last week , remove the mesh in the grill . Feel up inside for the nut that holds it in place .
Undo with a nut runner ( i think its m4) and then you'll have to very carefully prize the badge off . it is stuck with an adhesive pad though
you ll end up breaking the badge so just order a new one from a main dealer . mine cost me £12
make sure you get the correct badge , there are two sizes , early 4200 , and late 4200 face lift and GS ( which are bigger )